This invention relates to a beam forming network of the type which employs a matrix of coupling elements to link individual elements of an antenna to the different phase terminals of a phase combiner or phase splitter, hereinafter referred to as a phase combiner.
In a beam forming network of the above type unwanted interactions between the various conductive components need to be taken into consideration when selecting the values of the coupling elements, which will usually be resistive elements. However these interactions are unpredictable and therefore cannot be taken into consideration during initial calculation of their values. The procedure has therefore been adopted of initially selecting values for the coupling elements according to a calculation which ignores the aforementioned interactions; performing an experiment to determine the actual gain characteristcs, i.e., beam shape, obtained; calculating required changes to the values to correct any discrepancies between the required and actual gain characteristics, and correcting the values of the coupling elements accordingly.
The step of calculating the required corrections has itself to ignore the effect of the parasitic interactions on the correction and so the correction made is unlikely to result in exactly the required correction to the antenna gain characteristics. The procedure described in the preceding paragraph therefore has to be repeated, possibly several times, before an acceptable approximation to the required beam shape is achieved.